RHESSI Hard X-ray Microflare Statistics

We present the first in-depth statistical survey of all X-ray microflares observed by RHESSI between March 2002 and March 2007, a total of 25,705 events. These microflares were found using a new flare-finding algorithm designed to search the 6--12~keV count rate when RHESSIs full sensitivity was available in order to find the smallest events. These microflares are small flares, from low GOES C Class to below A Class (background subtracted) and associated with active regions. Each microflare is automatically analyzed at the peak time of the 6--12~keV emission. Spectral parameters are determined both by considering ratios between energy channels and by forward fitting a thermal plus non-thermal model. Flare images are created using back-projection and centroids and by forward fitting the complex visibilities. The combination of imaging and spectral parameters allow for the first time analysis of the thermal and non-thermal energy at the peak time of these microflares.